The present invention relates to a control valve used in a variable displacement compressor that forms a refrigerant circulation circuit in a vehicle air conditioner, and the displacement of which is variable on the basis of the pressure of the crank chamber.
In general, the refrigerant circulation circuit of a vehicle air conditioner includes a condenser, an expansion valve, which serves as a decompression device, an evaporator and a compressor. The compressor draws and compresses refrigerant from the evaporator, and discharges compressed gas to the condenser. The evaporator transfers heat to the refrigerant from the air in the vehicle. Because the heat of the air passing by the evaporator is transferred to the refrigerant flowing in the evaporator according to the magnitude of the thermal load, or the cooling load, the cooling gas pressure at the exit or downstream of the evaporator reflects the magnitude of the cooling load.
In a typical vehicle variable displacement swash plate type compressor, there is a displacement control mechanism to maintain the exit pressure of the evaporator (called the suction pressure) at a prescribed target value (called the set suction pressure). The displacement control mechanism uses feedback control to control the displacement of the compressor, i.e., the swash plate angle, and the suction pressure is a control indicator to achieve a refrigerant flow rate that meets the demand for cooling.
A typical example of the aforementioned displacement control mechanism is a control valve known as an inner control valve. The swash plate angle is determined through adjustment of the pressure (crank pressure) of the swash plate chamber (known also as the crank chamber) by sensing the suction pressure with a pressure-sensitive member such as bellows or a diaphragm, and adjusting the degree of valve opening by using of the displacement of the pressure-sensitive member for positioning the valve body.
There is a simple inner control valve that can have only a single set suction pressure and cannot finely control air conditioning control. This valve is known as a set suction pressure variable type control valve and is capable of changing the set suction pressure by electric control. The set suction pressure variable type control valve changes the set suction pressure by, for example, adding an actuator for applying a variable force to the inner control valve and thus changing (increasing or decreasing) a force acting on the pressure-sensitive member. This determines the set suction pressure of the inner control valve externally. The actuator may be, for example, an electromagnetic solenoid.
In the displacement control using an absolute value of the suction pressure as an indicator, however, a change in the set suction pressure by electric control does not necessarily change the actual suction pressure to the set suction pressure. That is, whether or not the actual suction pressure responsively follows a change in the setting of the set suction pressure is affected by the thermal load condition in the evaporator. As a result, although electric control finely adjusts the set suction pressure, the change in the displacement of the compressor tends is delayed. That is, the displacement does not always change continuously and smoothly.
It is an object of the present invention to provide a control valve for a variable displacement compressor that permits improvement of controllability or response of the displacement.
To achieve the foregoing and other objectives and in accordance with the purpose of the present invention, a control valve used in a variable displacement compressor is provided. The compressor draws refrigerant from an external refrigerant circuit, compresses the refrigerant and then discharges the compressed refrigerant to the external refrigerant circuit. A zone that is exposed to suction pressure is connected to a crank chamber by a bleeding passage, and a zone that is exposed to discharge pressure is connected to the crank chamber by a supply passage, thereby adjusting the pressure in the crank chamber. The displacement of the compressor is varied based on the pressure in the crank chamber. The control valve includes a valve housing, a valve chamber, a valve body, a first limiting member, a first urging member, a pressure-sensitive member, first and second pressure monitoring points, a second limiting member, a second urging member and a control member. The valve chamber is defined in the valve housing and forms a part of the supply passage or the bleeding passage. The valve body is accommodated in the valve chamber and is moved in the valve chamber to adjust the degree of opening of the supply passage or the bleeding passage. When contacting the valve body, the first limiting member limits the movement of the valve body. The first urging member urges the valve body toward the first limiting member. The pressure-sensitive chamber is defined in the valve housing. The pressure-sensitive member is movably arranged in the pressure-sensitive chamber and divides the pressure-sensitive chamber into a first pressure chamber and a second pressure chamber. The pressure-sensitive member is moved based on the pressures in the first and second pressure chambers. The pressure-sensitive member selectively separates from and engages with the valve body. The first and second pressure monitoring points are located in the external refrigerant circuit. The pressure difference between the two pressure monitoring points represents the compressor displacement. The first pressure monitoring point is located in a higher pressure zone and the second pressure monitoring point is located in a lower pressure zone. The first pressure chamber is exposed to the pressure at the first pressure monitoring point and the second pressure chamber is exposed to the pressure at the second pressure monitoring point. When the pressure-sensitive member is moved based on the pressure difference between the first and second pressure chambers, the movement of the pressure-sensitive member affects the position of the valve body such that the compressor displacement is changed to reduce fluctuations in the pressure difference between the first and second pressure chambers. When contacting the pressure-sensitive member, the second limiting member limits the movement of the pressure-sensitive member. The second urging member urges the pressure-sensitive member toward the second limiting member. The control member urges the valve body against the forces of the first and second urging members such that the valve body contacts the pressure-sensitive member. The force applied to the valve body is externally controlled so that a set pressure difference, which is a reference value for determining the position of the valve body by the pressure-sensitive member, is changed.
Other aspect and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.